The present invention relates to a vacuum power brake booster composed of a vacuum casing, which is subdivided by at least one movable partition wall into at least one vacuum chamber and at least one working chamber, and of a partition wall which is connected to an axially movable control hub that contains a valve assembly, the control hub acting upon a force-delivering member via a reaction device.
From German printed and published patent application No. 29 18 908, a vacuum power brake booster for automotive vehicles is known which incudes a vacuum casing which is subdivided into a vacuum chamber and a working chamber by a rigid partition wall that is movable together with a control hub. Channels for air circulation are contained in the control hub to connect the hollow interior chamber of the control hub, wherein a valve assembly controlling the air circulation is arranged, to the vacuum chamber and the working chamber. The control hub accommodates a longitudinally slidable valve piston whose pedal-side end cooperates with a poppet valve. For this purpose, the valve piston comprises a valve plate with a sealing edge forming an annular bead and coacting with the end surface of the poppet valve that is close to the booster casing. This known power brake booster bears the disadvantage that disturbing noise is caused upon actuation of the valve assembly, the atmospheric air flows through the control hub and enters the working chamber. The air first penetrates the poppet valve in an axial direction, while subsequently it flows radially outwardly with the valve passage opened between the valve piston and the poppet valve and the air finally enters into the channel leading to the working chamber after having once more changed its direction in an abrupt manner.